1. Field of the Invention
This invention relates to the construction of railway track, and in particular to the emplacement of sleepers on the track bed prior to the affixture of rails to the sleepers.
2. Description of the Prior Art
Traditionally, sleepers have been manhandled into place during the construction of new railway track. This is laborious, slow and, therefore, expensive. Furthermore the accuracy of placement depends entirely on the care taken by the persons doing the laying, and, having regard to the difficulty of manually shifting a sleeper, it is not surprising that in many cases the end result leaves something to be desired.
Attempts to improve on purely manual methods include manually attaching a plurality (say six) sleepers to a jig adapted to hold them in a correctly spaced and aligned array, and then depositing the array as a unit by means of a mobile crane or the like. This method is still labour intensive and still requires care in the positioning of each array. Furthermore, it suffers from the fact that each individual array is straight and therefore not appropriate for curved sections of track. Nevertheless, this technique is still widely used.
In view of the deficiencies of the largely manual methods referred to above, track laying machines have been developed, that are intended to more or less fully automate the process of laying sleepers. Such prior known machines are large and complex items. They usually advance on the track they lay, and therefore run on track wheels and are not independently steerable. Thus they cannot travel by road and have to be partially dismantled for road transport between one operation and another. They are costly to make and constitute considerable idle capital if not fully occupied.
Those prior known machines have usually included devices for depositing the individual sleepers which lift the sleeper into place while it is resting on carry arms or held by clamping devices that then have to be retracted from underneath the sleeper. This has usually required a specially prepared grooved bed to be formed, so as to provide clearance for the carry arms, and subsequently rectified. This has added to the complexity of the process and has limited the use of known machines to operations in which the track bottom ballast has been trucked to site and pre-deposited; whereas it is more economic to deliver all the ballast by train travelling slowly on the unballasted track.
All in all, prior known sleeper laying machines cannot be justified on a cost basis, except, maybe, for very large track construction jobs.